1. Field of the Invention
The present invention relates to a high pressure fuel pump control apparatus for an engine that serves to inject fuel into individual cylinders while controlling the fuel pressure in an accumulator to a target pressure, and more particularly, to a new technique for controlling the delivery of a maximum amount of fuel from a high pressure fuel pump.
2. Description of the Related Art
In recent years, there have been proposed engines in which the pressure of fuel in an accumulator is controlled to a high pressure value so as to inject the fuel in an atomized state (see, for example, a first patent document (Japanese patent application laid-open No. 2002-188545) and a second patent document (Japanese patent application laid-open No. H8-303325)).
Hereinafter, an example of the construction of a fuel system in such a kind of engine will be described.
A high pressure fuel pump for pressurizing the fuel to be injected to a high pressure is provided with a plunger that reciprocates in a pressure chamber in synchronization with the rotation of a camshaft of the engine, with a lower end of the plunger being arranged in pressure contact with a pump cam mounted on the camshaft. With such an arrangement, as the pump cam rotates in conjunction with the rotation of the camshaft, the plunger is caused to reciprocate in the pressure chamber, whereby the volume of the pressure chamber is changed to expand or contract.
In addition, a high pressure passage (delivery passage) downstream of the pressure chamber is connected with an accumulator through a delivery valve ( check valve) that permits the fuel to pass only in a direction from the pressure chamber toward the accumulator, whereby the accumulator holds the fuel delivered from the pressure chamber and distributes it to fuel injection valves.
Further, a low pressure passage upstream of the pressure chamber is connected with a fuel tank through a normally open flow control valve, a low pressure fuel pump and a low pressure regulator, so that the fuel drawn up from the low pressure fuel pump into the low pressure passage is adjusted to a predetermined feed pressure by the low pressure regulator, and then it is sucked into the pressure chamber through the flow control valve that is opened in a descending period in which the plunger moves downward from top dead center (TDC) up to bottom dead center (BDC) (i.e., a period in which the volume of the pressure chamber expands).
On the other hand, in an ascending period (i.e., a period in which the volume of the pressure chamber contracts) in which the plunger moves upward from the bottom dead center up to the top dead center, when the normally open flow control valve is closed, a maximum amount of fuel pressurized in the pressure chamber is delivered to the accumulator in accordance with the upward movement of the plunger.
In addition, when the flow control valve is not opened at all in the ascending period of the plunger in the high pressure fuel pump, the fuel sucked into the pressure chamber is relieved to the low pressure passage, so it is not delivered to the accumulator.
Moreover, when the flow control valve is closed during the ascending period of the plunger, a part of the fuel sucked into the pressure chamber is relieved into the low pressure passage for a period of time from the bottom dead center of the plunger until the arrival of the flow control valve at its closed position, and subsequently, the fuel left in the pressure chamber is pressurized and delivered into the accumulator for a period of time from the closed position of the flow control valve until the arrival of the plunger at its top dead center.
Thus, by controlling to close the flow control valve at arbitrary timing during the ascending period of the plunger, the amount of fuel delivered to the accumulator can be adjusted to an arbitrary amount between from a maximum amount of delivery to a minimum amount of delivery. Here, note that the normally open flow control valve has a normally deenergized solenoid built therein, so it is driven to close upon energization of the solenoid.
Hereinbelow, detailed reference will be made to the relation between a target closed position (hereinafter simply referred to as a “closed position”) TVC of the flow control valve and an amount of delivery fuel Q delivered from the high pressure fuel pump to the accumulator, in the ascending period of the plunger (from the time point of arrival at bottom dead center BDC to the time point of arrival at top dead center TDC) while referring to a timing chart in FIG. 10.
In FIG. 10, the axis of abscissa represents a time base (advance angle side-retard angle side) corresponding to the closed position TVC of the flow control valve, and the axis of ordinate represents, in the order from top to bottom, the active position of the plunger in the high pressure fuel pump (i.e., the ascending period from the bottom dead center BDC to the top dead center TDC being shown herein), energization timing TON of the solenoid (and interruption timing TOFF), the opened/closed state of the flow control valve, the internal pressure of the pressure chamber in the high pressure fuel pump (a pressure value Pa that acts as a valve-closing urging force on the flow control valve), and an amount of delivery fuel Q (a maximum amount of delivery fuel OMAX, an amount of relieved fuel QR, and a target amount of delivery fuel QO).
In FIG. 10, there is shown, as an example, an operation state of the flow control valve at the time when the closed position TVC of the flow control valve is controlled to a substantially midpoint from the time point of arrival of the plunger at the bottom dead center BDC to the time point of arrival thereof at the top dead center TDC.
That is, the energization timing of the solenoid in the flow control valve and the opened/closed state of the flow control valve are controlled in such a manner that the flow control valve is closed at a time point corresponding to the closed position TVC of the flow control valve, and the internal pressure of the pressure chamber is pressurized corresponding to the closed position TVC of the flow control valve.
In the amount of delivery fuel in FIG. 10, a range QR indicated by a broken line arrow represents the amount of fuel relieved to the low pressure passage (an amount of relieved fuel), a range QO indicated by a solid line arrow represents the amount of fuel actually delivered to the accumulator (a target amount of delivery fuel), and the target amount of delivery fuel QO is represented by a difference (QMAX-QR) between the maximum amount of delivery fuel QMAX and the amount of delivery fuel QR.
The maximum amount of delivery fuel QMAX is the amount of fuel sucked to the pressure chamber during the downward movement of the plunger (corresponding to the maximum amount of delivery fuel that can be supplied to a fuel rail).
An unillustrated ECU (electronic control unit) specifies the time point of arrival of the plunger at the bottom dead center BDC based on the rotational position of the engine, and determines, as a time point corresponding to the closed position TVC of the flow control valve, a time point at which a first or former half period Tr has elapsed from the time point of arrival of the plunger at the bottom dead center BDC.
In addition, in order to close the flow control valve at the time point corresponding to the closed position TVC, an energization start time point TON and an energization end time point TOFF for the solenoid of the flow control valve are controlled as energization timings of the solenoid.
At this time, there exists an operation delay time Tp from the start of energization of the solenoid to the completion of closing of the flow control valve, so the energization of the solenoid is started at a time point TON going back by the operation delay time Tp from the time point corresponding to the target closed position TVC.
Also, since the operation delay time Tp is changed mainly depending on the electrical energy supplied to the solenoid, it is stored in a memory in the ECU beforehand as data for individual battery voltages so that an appropriate time is set in accordance with the battery voltage actually detected upon energization of the solenoid. As a result, even if the battery voltage varies, it is possible to control the closed position TVC of the flow control valve with a high degree of precision.
Hereinafter, when the operation delay time Tp has elapsed from the start of energization of the solenoid, the flow control valve completes its valve closing operation (TVC), whereafter the fuel in the pressure chamber is pressurized by an upward movement of the plunger in the high pressure fuel pump, so that the fuel pressure in the pressure chamber itself acts as a valve-closing urging force (≧Pa) sufficient to maintain the flow control valve in its closed state.
The valve-closing urging force due to the fuel pressure in the pressure chamber at this time continues up to a time point just before the time point of arrival of the plunger at the top dead center TDC at which the pressure in the pressure chamber begins to be reduced.
Accordingly, after the fuel pressure in the pressure chamber has risen above the pressure value Pa that acts as the valve-closing urging force enough to close the flow control valve after the closure of the flow control valve, it is possible to maintain the closed state of the flow control valve over a period up to around the time point TDC of arrival of the plunger at the top dead center even without continuing to apply the electromagnetic valve-closing urging force due to the energization of the solenoid.
Thus, in a second patent document, power consumption is intended to be reduced by setting an energization holding time Th, for which the energization of the solenoid is continued after the arrival of the flow control valve at the closed position TVC, to a minimum time that will be required from the time point of arrival of the flow control valve at the closed position TVC to the time the fuel pressure in the pressure chamber itself rises above the pressure value Pa that acts as the valve-closing urging force of the flow control valve.
When the flow control valve is closed at its target closed position TVC, a part of the amount of fuel (=QMAX ), which has been sucked from the low pressure passage to the pressure chamber during the downward or descending movement of the plunger immediately before it (a plunger operation position at an advance angle side from the bottom dead center BDC), is relieved through the opened flow control valve to the low pressure passage as the amount of relieved fuel QR in the ascending period (the first half period Tr in FIG. 10) from the time point of arrival of the plunger at the bottom dead center BDC to the time point of arrival thereof at the closed position TVC.
On the other hand, the flow control valve is closed for a period from the closed position TVC to the time point of arrival of the plunger at the top dead center TDC (a second or latter half period To), so an amount of fuel (=QMAX-QR) left in the pressure chamber at the closed position TVC is pressurized so as to be delivered to the accumulator through the delivery valve as the target amount of the delivery fuel QO.
In addition, for example, when the time point (Tr=0) of the plunger bottom dead center BDC that is the position of the most advance angle side in the plunger ascending period (Tr+To) is decided as the closed position TVC, the flow control valve is closed in the entire plunger ascending period, so the entire amount of fuel (=QMAX) sucked into the pressure chamber is pressurized and delivered to the accumulator as the maximum amount of delivery fuel QMAX.
On the other hand, when the solenoid has not been energized at all in the plunger ascending period, the normally open flow control valve remains opened in the entire plunger ascending period, so the entire amount of fuel (=QMAX) sucked into the pressure chamber is relieved to the low pressure passage, and pressurized fuel is not delivered to the accumulator at all.
Thus, by controlling the closed position TVC to an arbitrary position between from the plunger bottom dead center BDC to the plunger top dead center TDC, it is possible to adjust the amount of fuel to be delivered to the accumulator to an arbitrary amount from the maximum amount of delivery fuel QMAX to the minimum amount of delivery fuel (=0).
The ECU determines a target pressure in accordance with the operating condition of the engine (the number of revolutions per minute of the engine, the amount of depression of an accelerator pedal, etc.), and calculates the target delivery amount QO of the fuel to be delivered to the accumulator through a feedback arithmetic calculation (e.g., PID calculation, etc.) based on a pressure deviation between the value of the fuel pressure in the accumulator. detected by the fuel pressure sensor and the target pressure.
Moreover, the ECU determines a time (or angle) Tr from the position of arrival of the plunger at the bottom dead center BDC based on the relation between the closed position TVC of the flow control valve and the amount of delivery fuel Q (the characteristics of FIG. 10), and controls the actual closed position TVC.
Next, detailed reference will be made to a general control operation when the maximum amount of fuel QMAX is delivered from the high pressure fuel pump while referring to a timing chart (solid lines) in FIG. 11.
In FIG. 11, the axis of abscissa represents a time base, similarly as stated above (FIG. 10), and the axis of ordinate represents, in the order from the top to the bottom, a reference signal REF generated based on the rotational position of the engine, the operation position of the plunger in the high pressure fuel pump, the energization timing of the solenoid in the flow control valve, the opened/closed state of the flow control valve, and the internal pressure in the pressure chamber of the high pressure fuel pump. Here, note that in the operating position of the plunger in FIG. 11, solid lines represent a normal plunger operation, and broken lines represent a plunger operation shifted to a retard angle side.
In FIG. 11, first of all, the ECU generate the reference signal (pulse) REF that indicates a predetermined rotational position in the rotational phase of the engine.
Here, note that the positional relation between the position of the reference signal REF and the position of arrival of the plunger at the bottom dead center BDC that is reached thereafter is stored beforehand in the memory of the ECU as design values, and a time point at which an offset value Td (corresponding to a predetermined time or a predetermined angle) has elapsed from the reference signal REF is specified as the position of arrival of the plunger at the bottom dead center BDC.
Hereinafter, the bottom dead center BDC estimated by the ECU based on the design values is called an “estimated bottom dead center BDC”. That is, the ECU recognizes the operation characteristics of the plunger represented by the solid lines in FIG. 11 as the normal operation position of the plunger, and decides, as the target closed position TVC, the same position (i.e., a position of Tr=0) as the estimated bottom dead center BDC when the maximum amount of delivery fuel QMAX (see FIG. 10) is controlled.
The ECU starts to energize the solenoid at the time point TON going back by the operation delay time Tp from the closed position TVC, and terminates the energization of the solenoid at the time point TOFF at which the energization holding time Th has elapsed from the closed position TVC (i.e., at a time point at which the internal pressure of the pressure chamber has reached Pa or higher).
As a result, like the opened/closed state of the flow control valve indicated by a solid line in FIG. 11, the flow control valve is closed at the position of the estimated bottom dead center BDC of the plunger, and the fuel in the pressure chamber is pressurized in the plunger ascending period therefrom to the time point of arrival of the plunger at the top dead center TDC so that the maximum amount of fuel QMAX is delivered to the accumulator.
However, the ECU controls the closed position TVC of the flow control valve in a feedback manner according to a PID calculation based on the pressure deviation between the target pressure determined in accordance with the operating condition of the engine and the fuel pressure in the accumulator, as previously stated above.
Thus, when there occurs a situation in which the fuel pressure in the accumulator is much lower than the target pressure, the amount of feedback correction becomes excessively large so there is a possibility that the closed valve position TVC might pass the estimated bottom dead center BDC toward the advance angle side. In this case, there is a fear that it might become unable to ensure the energization holding time Th that is required to maintain a minimum amount of energization during the ascending period of the plunger, thus making it impossible to control the amount of fuel to be delivered.
Accordingly, in the first patent document (see claim 2), the position of the estimated bottom dead center BDC is decided as an advance angle limiting position LIM (=L0), as shown in FIG. 11, so that the closed position TVC is limited or prevented from being controlled to a position more advanced than the advance angle limiting position LIM (=L0).
As shown in FIG. 11, in a conventional apparatus, in case where the positional relation between the reference signal REF and the estimated bottom dead center BDC that is arrived at thereafter coincides with the design values stored beforehand in the ECU, there will be any problem when the maximum amount of fuel QMAX is delivered from the high pressure fuel pump to the accumulator.
In an actual control apparatus, however, it is considered that the positional relation of the reference signal REF and the estimated bottom dead center BDC that is arrived at thereafter might shift from a normal relation due, for example, to the variations of those parts which are associated with position control such as the assembly positions of the high pressure fuel pump and a cam angle sensor for detecting the rotational position of a cam, the machining accuracy of a pump cam, etc.
However, since in the above-mentioned conventional apparatus, no special consideration is made with respect to the variations of those parts which are associated with the position control of a fuel supply system, there are the following problems.
Hereinafter, specific reference will be made to problems arising when the maximum amount of fuel QMAX is caused to be delivered from the high pressure fuel pump with the occurrence of the variations of the parts associated with position control while referring to FIG. 11, similarly as described above.
Here, note that the characteristics represented by broken lines in FIG. 11 show the operation positions of the plunger when the plunger generates a maximum deviation in the retard angle direction.
The actual bottom dead center BDC1 when the operation position of the plunger generates a maximum deviation to the retard angle side (broken line) shifts by the maximum amount of deviation Trtd to the retard angle side from the estimated bottom dead center BDC when the plunger operates at normal timing (solid line).
In this case, since the ECU does not detect the deviation of the operation position of the plunger even though the plunger operation position has shifted from the normal position, the time point after only the offset value Td has elapsed from the reference signal REF is specified as the estimated bottom dead center BDC assuming that the plunger is in the normal operation position.
Accordingly, in order to deliver the maximum amount of delivery fuel QMAX to the accumulator, the closed position TVC is controlled until the position of Tr=0 (i.e., the same position as the estimated bottom dead center BDC) is made as the advance angle limiting position LIM (=L0).
As a result, the ECU starts to energize the solenoid at the time point TON going back by the operation delay time Tp from the closed position TVC, and terminates the energization of the solenoid at the time point TOFF at which the energization holding time Th has elapsed from the closed position TVC.
However, the actual bottom dead center BDC1 in the actual operation position of the plunger is shifted by the maximum amount of deviation Trtd to the retard angle side from the estimated bottom dead center BDC.
Therefore, in the example of FIG. 11, the energization of the solenoid has been terminated before the plunger arrives at the actual bottom dead center BDC1, so the energization holding time Th for which the solenoid is originally to be energized after the closure of the flow control valve in the ascending period of the plunger can not be ensured.
Accordingly, fuel will pass through the normally open flow control valve which is not closed in the ascending period of the plunger (the opened/closed state of the flow control valve indicated by the broken line in FIG. 11), as a consequence of which the fuel sucked into the pressure chamber is relieved to the low pressure passage through the flow control valve that remains in the open state, and hence the fuel is not delivered to the accumulator.
In the conventional high pressure fuel pump control apparatus for an engine, in cases where the plunger generates the maximum amount of deviation Trtd in the retard angle direction resulting from variations associated with the position control of the flow control valve, when the maximum amount of delivery fuel QMAX is to be delivered to the accumulator, the energization to the solenoid is terminated based on the estimated bottom dead center BDC more advanced than the actual bottom dead center BDC1, so there might occur a situation where delivery control becomes impossible.
Thus, there arises the following problems. That is, when the maximum amount of delivery fuel QMAX is controlled to be delivered, there occurs a situation in which fuel delivery control becomes unable to be done due to variations associated with the position control of the flow control valve, so a required amount of fuel can not be delivered to the accumulator, and hence the fuel pressure in the accumulator can not be maintained at the target pressure, making it impossible to obtain desired combustion performance and inducing deterioration in drivability and the exhaust gas.